The introduction of molecular sieve type cracking catalysts resulted in a dramatic improvement in cracking activity and selectivity of the catalyst. The molecular sieves are found to have intrinsic activity for cracking far greater than the conventional silica alumina cracking catalysts that were in use at the time of the introduction of the molecular sieve type catalyst.
There are several patents describing processes for preparing these zeolites. U.S. Pat. No. 3,692,655, for example, covers a method for preparing a faujasitic type zeolite that is stabilized by cation and thermal stabilization. The older more conventional cracking catalysts are described in Patents such as U.S. Pat. No. 3,404,097 to Wilson et al. which describes a silica-magnesia-fluoride catalyst. U.S. Pat. No. 3,650,988 of Magee et al. covers a process for preparing a hydrocarbon cracking catalyst containing a semi-synthetic portion, i.e., clay, silica-alumina and a zeolite portion. There are several other patents describing processes of preparing molecular sieve type catalyst. U.S. Pat. No. 3,425,956 of Baker et al. is typical of a large body of art in this area.
U.S. Pat. No. 3,867,308 to Elliot describes a process for preparing a hydrocarbon cracking catalyst by preparing a hydrosol by rapid addition of mineral acid to sodium silicate, adjusting the pH of the hydrosol, adding clay and zeolite components, spray drying, washing with water, rare earth exchanging and recovering the product.
In the process covered in the instant application the basic process is modified by the addition of titanium, zirconium, iron or quadrivalent cerium salts to the hydrosol to improve the qualities of the final product.